As much of a surprise as it may be to you Riot is more concerned about preventing performance issues in the huge amount of actual games with multiple players than your ability to test out builds while the servers are being heavily taxed. Buck up and test your builds the 90 or so % of the time that custom games aren't limited in this way instead of being such a selfish little whiner.

Ah I thought they did this in the previous patch as a perminent thing. Fair enough I admit I was ignorant however it wouldn't be a problem if they actually announced this and explained that it was temporary while they worked on the servers